The present invention is directed to a touch screen user input device for a computer and, in particular, to a touch screen having reduced noise while providing high resolution.
Touch screens for computer input permit a user to write or draw information on a computer screen or select among various regions of a computer generated display, typically by the user""s finger or by a free or tethered stylus. The cost of touch screen displays is partly dependent on the resolution which is desired. When the application requires only gross resolution (such as determination, within about two inches or more, of the position of the finger or stylus on the screen) only moderate expense is typically involved. However, when fine resolution is required (i.e., resolution less than about one inch, preferably less than about xc2xd inch, more preferably less than about xc2xc inch and most preferably less than about xe2x85x9 inch), the expense of touch screens provided according to previous approaches has been relatively high. One reason for the expense is that additional hardware or methods were needed to distinguish the small signals representing fine-resolution positions or movements from noise (i.e., signals which are not indicative of the position of the finger or stylus). Many previous devices have also been relatively expensive to linearize (i.e., to derive an indication of the location of the finger or stylus based on the output signal from the device). Typically, the position is a non-linear function of the output signal. It is believed that the linearization process, in some previous devices, involves manually modifying the size or shape of screen electrodes. Since this must be individually done for each screen overlay which is produced, the expense can be high.
Another contributor to the high expense of high-resolution touch screens is the need, in some processes, to provide electrodes or other deposited layers on both the front and rear surfaces, and/or to provide two or more separate vacuum processing steps. Further, when the final product is made by positioning or bonding a separate overlay to a computer screen (typically a cathode ray, tube or CRT) this additional step adds further expense to the final product.
Accordingly, it would be useful to provide a touch screen which provides fine resolution while reducing or eliminating noise at a reduced or low cost.
The present invention provides a low-noise, high-resolution touch screen. According to one embodiment, in order to provide reduction or elimination of noise, which is particularly troublesome for fine resolution devices, a relatively high sampling rate is provided along with a filter which distinguishes signal from the (typically low-frequency) noise. Furthermore, one embodiment of the invention can distinguish the desired signal from spurious signals, such as a grounding or static discharge, by using automatic gain control.
Linearization of the signal includes a measurement of signals from touches at various known screen locations and a conversion from the output signal to the derived finger or stylus location using the measured data, thus eliminating the need for manual or individual changing or xe2x80x9ctuningxe2x80x9d of electrodes or other features of the screen.
According to one embodiment of the invention, electrodes are placed directly on a CRT or other computer screen. By xe2x80x9cdirectlyxe2x80x9d is meant that the electrodes are in contact with the CRT, rather than on an overlay which is later bonded to the screen. One embodiment permits the electrodes to be positioned so as to eliminate rear-surface electrodes or layers and so to eliminate one or more vacuum processing steps, preferably requiring only a single vacuum processing step to make a computer screen into a touch screen.
Touch screens according to the present invention can be used for a number of purposes. One purpose involves use for an electronic gaming machine such as an electronic slot machine, an electronic keno machine, and the like. Other uses include uses for ordinary computing, such as computing on a personal computer, laptop computer, palmtop computer, notepad computer, personal communication device, telephone, interactive television and the like, running software such as word processing, spreadsheet, communications, database, programming, networking, and other well-known software. The invention can be used in connection with custom-written software, or in connection with computer operating systems designed for pen computing, such as Penpoint(trademark) of GO Corporation, Windows for Pen Computing(trademark) of Microsoft Corporation, or with operating systems or other software intended for use with a pointing device such as a mouse, trackball, joystick and the like.